Nonradiative Fluorescence Resonance Energy Transfer Research Articles

Interaction of Ibuprofen with Partially Unfolded Bovine Serum Albumin in the Presence of Ionic Micelles and Oligosaccharides at Different λex and pH: A Spectroscopic Analysis.

The interaction between the plasma protein bovine serum albumin (BSA) and the drug ibuprofen (IBU) has been investigated at three different pH values (7.4, 6.5, and 8.0) in the presence of oligosaccharides and surfactants. The interaction analysis of BSA with oligosaccharides and surfactants has also been studied in the absence of the drug ibuprofen. The results obtained give convenient and efficient access to understand the mechanism of binding of ibuprofen to BSA, and the major forces involved are found to be hydrophobic forces, hydrogen bonding and ionic interactions. In addition to that, the formation of inclusion complexes of ibuprofen with oligosaccharides (β-CD and 2-HP-β-CD) has been observed, which has depicted that due to the hydrophobic nature of ibuprofen, it becomes more soluble in the presence of oligosaccharides, but due to the larger size of the inclusion complexes, these could not be able to access the hydrophobic pocket of BSA where tryptophan-212 (Trp-212) resides. The binding interaction between BSA and ibuprofen is observed in the presence of surfactants (SDS and CTAB), which partially unfold the protein. Non-radiative fluorescence resonance energy transfer (FRET) from Trp and Tyr residues of BSA in the presence of an anionic surfactant SDS to ibuprofen has depicted that there is a possibility of drug binding even in the partially unfolded state of BSA protein. Furthermore, the distance between the protein and the drug has been calculated from the FRET efficiency, which gives a comprehensive overview of ibuprofen binding to BSA even in its partially denatured state. The hydrophobic drug binding to the partially unfolded serum albumin protein (BSA) supports the "necklace and bead structures" model and opens up a new direction of drug loading and delivery system, which will have critical therapeutic applications in the efficient delivery of pharmacologically prominent drugs.

FRET probe for selective and sensitive detection of vitamin A by cadmium free quantum dots (ZnS).

Vitamin A as a powerful antioxidant plays an important role in human body functions including bone remodeling regulation, healthy immune system and cell growth reproduction. An accurate determination of vitamin A is taken into consideration because of its importance for human health. In this paper, we reported a fluorescence resonance energy transfer (FRET) probe, MPS-capped ZnS QDs, for sensitive and selective detection of vitamin A. The colloidal MPS-capped ZnS QDs were prepared from Zinc acetate and sodium sulfide by employing 3-mercaptopropyltrimethoxysilane (MPS) molecules as the stabilizer or capping agent at the pH condition of 10. The synthesized MPS-capped ZnS QDs were characterized by means of FT-IR, UV-Vis, DLS, and TEM techniques. The sensing behavior of MPS-capped ZnS QDs for selective and sensitive detection of vitamin A, vitamin B2, vitamin B6, vitamin E, vitamin K, vitamin H, vitamin D3 and vitamin C was investigated using fluorescence spectroscopy. The detection mechanism involves photoinduced charge transfer from the surface of ZnS QDs to Vitamin resulting in the fluorescence quenching of ZnS QDs followed by nonradiative fluorescence resonance energy transfer. An excellent selectivity was observed for vitamin A versus other tested species. A linear relationship was observed between the fluorescence intensity of MPS-capped ZnS QDs and the concentration of vitamin A in the range of 3.33-36.66μM with detection limit of 1.062μM.

Study on the molecular recognition action of lamivudine by human serum albumin.

In this work, the interaction of an anti-HIV drug lamivudine and human serum albumin (HSA) was studied by multispectroscopic and molecular modeling methods. The fluorescence emission spectra showed that the fluorescence of HSA was quenched by lamivudine through static mechanism with HSA-lamivudine complex produced at ground state. According to the binding equilibriums observed at 4 different temperatures, the number of binding site, binding constant, enthalpy change, entropy change, and Gibbs free energy change of the interaction were calculated. The results indicated that there was only 1 main binding site under present concentration condition, and then, the location of this binding site was ascertained by molecular probe experiments using warfarin and ibuprofen as site markers. The interaction was a spontaneous and exothermic process. Hydrogen bonds and van der Waals force were the major power that fixed lamivudine on Sudlow's site I in subdomain IIA of HSA molecule. The distance between donor and acceptor was determined by Förster's nonradiative fluorescence resonance energy transfer theory. Circular dichroism spectra exhibited the alteration of HSA's secondary structures. Molecular modeling investigation revealed the structure of HSA-lamivudine complex, including the conformation of lamivudine in binding site, the amino residues close to lamivudine, and the interaction forces between receptor and ligand. The study may be beneficial to therapists in understanding the distribution of lamivudine in vivo and explaining its drug-resistant mechanism in clinical diagnosis.

Spectral focusing of broadband silver electroluminescence in nanoscopic FRET-LEDs.

Few inventions have shaped the world like the incandescent bulb. Edison used thermal radiation from ohmically heated conductors, but some noble metals also exhibit 'cold' electroluminescence in percolation films, tunnel diodes, electromigrated nanoparticle aggregates, optical antennas or scanning tunnelling microscopy. The origin of this radiation, which is spectrally broad and depends on applied bias, is controversial given the low radiative yields of electronic transitions. Nanoparticle electroluminescence is particularly intriguing because it involves localized surface-plasmon resonances with large dipole moments. Such plasmons enable very efficient non-radiative fluorescence resonance energy transfer (FRET) coupling to proximal resonant dipole transitions. Here, we demonstrate nanoscopic FRET-light-emitting diodes which exploit the opposite process, energy transfer from silver nanoparticles to exfoliated monolayers of transition-metal dichalcogenides. In diffraction-limited hotspots showing pronounced photon bunching, broadband silver electroluminescence is focused into the narrow excitonic resonance of the atomically thin overlayer. Such devices may offer alternatives to conventional nano-light-emitting diodes in on-chip optical interconnects.

A novel FRET probe for selective and sensitive determination of vitamin B12by functionalized CdS QDs in aqueous media: applications to pharmaceutical and biomedical analysis

Vitamin B12 (VB12) is one of the essential B complex vitamins, it is a water soluble nutrient and a medicine. Herein we developed, a novel but straightforward method for the selective and sensitive quantitative determination of VB12 based upon measuring the fluorescence quenching of functionalized CdS quantum dots (QDs) in aqueous media. The mercaptopropionic acid (MPA) functionalized CdS QDs were directly synthesized from cadmium chloride and sodium sulfide in aqueous media by a chemical method. The detection mechanism involves photoinduced charge transfer from CdS QDs towards VB12 at the surface of the CdS QDs resulting in the fluorescence quenching of CdS QDs followed by nonradiative fluorescence resonance energy transfer. Under the optimized conditions, the relationship between the fluorescence intensity of the CdS QDs and VB12 concentration was linear in the range of 5.0–100 μg mL−1 with a limit of detection of 6.91 μg mL−1. The selectivity experiment indicated excellent selectivity for VB12 over a number of interfering species. Moreover the method was successfully applied in the determination of VB12 in complex matrices, namely blood serum, urine and pharmaceutical formulations (multivitamin injection), without sample pretreatment. The accuracy and reliability of the method was further ascertained by recovery studies via the standard addition method with percentage recoveries in the range of 97.15%–99.49% being obtained. In addition, the probable fluorescence quenching mechanism of the CdS QDs induced by VB12 is also discussed.

Indirect activation of porphyrin by semiconductor quantum dots with two-photon excitation

Steady-state and nanosecond time-resolved spectroscopies are performed to investigate the interaction between CdSe quantum dots (QDs) and mesotetraphenylporphyrin (TPP) photosensitizers under two-photon excitation with 800-nm femtosecond laser pulses. The luminescent intensity and lifetime of the QDs decrease intensively in the QD-porphyrin mixture, whereas those of the TPP increase, suggesting occurence of a nonradiative fluorescence resonance energy transfer (FRET) process between the excited states of the donors and acceptors. An energy transfer efficiency of 0.27 is estimated from quenching of the excited-state radiative lifetime of the QDs. A 4-nm red shift in the emission spectrum of the CdSe QDs is observed after mixing with TPP, which is speculated to be caused by the energy transfer from QDs of small size to large. This study could be valuable for developing a QD-based drug system for application in two-photon excitation photodynamic therapy.

Two‐Photon Excitation of Quantum‐Dot‐Based Fluorescence Resonance Energy Transfer and Its Applications

Nonradiative fluorescence resonance energy transfer (FRET) between a luminescent quantum dot (QD) donor and a proximal dye brought in close proximity of the QD surface via conjugation with a dye-labeled peptide (or a protein) is shown (see figure). The system is excited with near IR irradiation (well below the absorption band of the QD), via a fast two-photon process, which produces a FRET signal with very low background contribution due to a substantially reduced nonlinear direct excitation of the dye.

Dual-Labeled Probes for Fluorescence and Electron Microscopy

Abstract Fluorescein and the 1.4 nm Nanogold cluster have been separately attached to polyclonal antibody Fab’ fragments to generate combined fluorescent and gold secondary antibody probes (1, 2), and in comparisons with Nanogold, colloidal gold and fluorescein-labeled secondary antibodies, neither label was found to be significantly compromised by the presence of the other. The proximity to a gold label with which a fluorophore retains sufficient fluorescence emission intensity to be useful is limited by non-radiative fluorescence resonance energy transfer (FRET) (3). This is a function of the degree of overlap of the fluorophore emission spectrum with the metal particle absorbtion spectrum, and of the separation of the metal particle and the fluorophore (4); for an effective dual-labeled probe, separation should be greater than the Forster distance (3), at which 50 % of excited-state decay occurs by FRET.

Preferential distribution of the fluorescent phospholipid probes NBD-phosphatidylcholine and rhodamine-phosphatidylethanolamine in the exofacial leaflet of acetylcholine receptor-rich membranes from Torpedo marmorata.

The distribution of the two fluorescent phospholipid analogs across acetylcholine receptor (AChR)-rich membranes from Torpedo marmorata has been studied by a combination of nonradiative fluorescence resonance energy transfer using fluorescent lipid probes and quenching of their fluorescence with Co2+ and 2,4,6-trinitrobenzenesulfonic acid. The fluorescent lipid analogs were supplied to the AChR-rich membrane or liposome suspension by simply injecting ethanol solutions of the probes into the medium. The efficiency of the fluorescence energy transfer between NBD-labeled phosphatidylcholine and rhodamine-labeled ethanolamine glycerophospholipids was measured in model membranes prepared in such a way that the probes could be targeted at the same or opposite halves of the bilayer, and the results were compared with those obtained for native AChR-rich membranes. It is shown that NBD-PC and Rho-PE can be efficiently (95%) incorporated into AChR-rich membranes and liposomes. On the basis of the comparison with model liposomes, the energy transfer experiments suggest a preferential exofacial location of the parental phospholipids in the native AChR-rich membrane. Fluorescence quenching with Co2+ and TNBS showed these two phospholipid analogs to be located predominantly in the outer leaflet of the bilayer in AChR-rich membranes. From the Co2+ quenching of the lipid analogs, it was also possible to calculate the surface potential of the outer leaflet of the membrane as being on the order of -15 mV.

Determination of the transbilayer distribution of fluorescent lipid analogues by nonradiative fluorescence resonance energy transfer.

We measured the nonradiative fluorescence resonance energy transfer between 7-nitro-2,1,3-benzoxadiazol-4-yl (NBD) labeled lipids (amine labeled phosphatidylethanolamine or acyl chain labeled phosphatidylcholine) and rhodamine labeled lipids in large unilamellar dioleoylphosphatidylcholine vesicles. Two new rhodamine labeled lipid analogues, one a derivative of monolauroylphosphatidylethanolamine and the other of sphingosylphosphorylcholine, were found to exchange through the aqueous phase between vesicle populations but not to be capable of rapid transbilayer movement between leaflets. Energy transfer from NBD to rhodamine was measured using liposomes with symmetric or asymmetric distributions of these new rhodamine labeled lipid analogues to determine the relative contributions of energy transfer between donor and acceptor fluorophores in the same (cis) and opposite (trans) leaflets. Since the characteristic R0 values for energy transfer ranged from 47 to 73 A in all cases, significant contributions from both cis and trans energy transfer were observed. Therefore, neither of these probes acts strictly as a half-bilayer quencher of NBD lipid fluorescence. The dependence of transfer efficiency on acceptor density was fitted to a theoretical treatment of energy transfer to determine the distances of closest approach for cis and trans transfer. These parameters set limits on the positions of the fluorescent groups relative to the bilayer center, 20-31 A for NBD and 31-55 A for rhodamine, and provide a basis for future use of these analogues in measurements of transbilayer distribution and transport.

Detection of nucleic acid hybridization by nonradiative fluorescence resonance energy transfer.

Three approaches were used to study hybridization of complementary oligodeoxynucleotides by nonradiative fluorescence resonance energy transfer. (i) Fluorescein (donor) and rhodamine (acceptor) were covalently attached to the 5' ends of complementary oligodeoxynucleotides of various lengths. Upon hybridization of the complementary oligodeoxynucleotides, energy transfer was detected by both a decrease in fluorescein emission intensity and an enhancement in rhodamine emission intensity. In all cases, fluorescein emission intensity was quenched by about 26% in the presence of unlabeled complement. Transfer efficiency at 5 degrees C decreased from 0.50 to 0.22 to 0.04 as the distance between donor and acceptor fluorophores in the hybrid increased from 8 to 12 to 16 nucleotides. Modeling of these hybrids as double helices showed that transfer efficiency decreased as the reciprocal of the sixth power of the donor-acceptor separation R, as predicted by theory with a corresponding R0 of 49 A. (ii) Fluorescence resonance energy transfer was used to study hybridization of two fluorophore-labeled oligonucleotides to a longer, unlabeled oligodeoxynucleotide. Two 12-mers were prepared that were complementary to two adjacent sequences separated by four bases on a 29-mer. The adjacent 5' and 3' ends of the two 12-mers labeled with fluorescein and rhodamine exhibited a transfer efficiency of approximately 0.60 at 5 degrees C when they both hybridized to the unlabeled 29-mer. (iii) An intercalating dye, acridine orange, was used as the donor fluorophore to a single rhodamine covalently attached to the 5' end of one oligodeoxynucleotide in a 12-base-pair hybrid. Under these conditions, the transfer efficiency was approximately 0.47 at 5 degrees C. These results establish that fluorescence modulation and nonradiative fluorescence resonance energy transfer can detect nucleic acid hybridization in solution. These techniques, with further development, may also prove useful for detecting and quantifying nucleic acid hybridization in living cells.